Fmoc-Arg(Pbf)-OH

Fmoc-Arg(Pbf)-OH is the standard derivative for the introduction of arginine residues into peptides via Fmoc solid‑phase peptide synthesis. The Pbf side‑chain protecting group in Fmoc-Arg(Pbf)-OH provides superior stability during chain assembly compared to earlier arginine protecting groups, with the Pbf group being removed with TFA approximately 1–2 times faster than Pmc, producing a clean, colorless final peptide product. The Fmoc protecting group in Fmoc-Arg(Pbf)-OH is orthogonal to the acid‑labile Pbf group, allowing for selective deprotection of the N‑terminus during chain assembly without affecting side‑chain protection. In the preparation of peptides containing both arginine and tryptophan, it is recommended that Fmoc-Arg(Pbf)-OH be used in conjunction with Fmoc‑Trp(Boc)-OH to prevent oxidation side reactions. The unique structural feature of Fmoc-Arg(Pbf)-OH is the Pbf group itself — a bulky, electron‑rich aromatic sulfonyl that efficiently blocks the nucleophilic guanidino nitrogen, preventing unwanted side reactions such as N‑to‑N migration, lactam formation, and intermolecular coupling during chain assembly. This makes Fmoc-Arg(Pbf)-OH a critical building block for synthesizing arginine-rich sequences, which are essential in protein interaction studies, cell‑penetrating peptides (CPPs), and therapeutic peptide development.

 Product Parameters

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Synthetic Route

Fmoc-Arg(Pbf)-OH is commercially prepared by first protecting the guanidino side chain of L‑arginine with the Pbf group, followed by Fmoc protection of the α‑amino group.

Step 1 — Pbf side‑chain protection of L‑arginine (guanidino protection):

Dissolve L‑arginine in an appropriate solvent system (e.g., water/dioxane or DMF). Add sodium carbonate to adjust the pH to alkaline conditions. Introduce the Pbf group by reacting with Pbf‑Cl (2,2,4,6,7-pentamethyldihydrobenzofuran-5-sulfonyl chloride) under controlled conditions. The Pbf group reacts selectively with the guanidino nitrogen to form the Nω‑Pbf‑protected arginine. Isolate the Pbf‑protected intermediate by neutralization, extraction, and precipitation.

Step 2 — Fmoc protection of the α‑amino group:

Dissolve Nω‑Pbf‑L‑arginine (1.0 eq) in a mixture of water and dioxane or acetone. Add sodium carbonate or sodium bicarbonate (2.0–2.5 eq) to adjust the pH to 8–9. Cool the solution to 0–5 °C. Add Fmoc‑Cl (1.05–1.1 eq) dissolved in dioxane dropwise over 30–60 minutes while maintaining the pH at 8–9 with additional base. Stir the mixture at room temperature for 2–4 hours.

Step 3 — Workup and isolation:

Dilute the reaction mixture with water and extract with diethyl ether to remove excess Fmoc‑Cl. Acidify the aqueous layer to pH 1–2 with concentrated HCl to precipitate the Fmoc‑protected product. Extract the product with ethyl acetate, wash the organic layer with water and brine, dry over anhydrous sodium sulfate, filter, and concentrate.

Step 4 — Purification:

Purify the crude product by recrystallization from a suitable solvent system or by silica gel column chromatography to obtain Fmoc-Arg(Pbf)-OH as a white to off‑white solid with the reported optical rotation and purity specifications.

Product Quality Assurance

Cosperpharm has established a comprehensive quality assurance system for Fmoc-Arg(Pbf)-OH that meets the rigorous expectations of both peptide intermediate manufacturing and impurity reference standard applications:

Thorough analytical characterization. Each batch undergoes multi‑technique analytical release testing: HPLC purity (≥98.0% industrial grade; ≥99.0% reference standard grade, with full chromatographic traceability), water content (Karl Fischer ≤2.0%), loss on drying (≤2.0% at 50°C), D‑enantiomer content (≤0.3% by chiral HPLC), specific optical rotation confirmation ([α]D = −7.1 to −3.1, c=1, DMF), appearance verification (white to off‑white powder to crystalline powder), residual solvent analysis (GC), solubility verification (10% in DMF — clear, colorless solution), and identity confirmation by IR.

Full batch traceability with retention samples. From raw material procurement (L‑arginine from qualified suppliers) through Pbf side‑chain protection, Fmoc protection, recrystallization, drying, and final packaging, every step is fully documented and traceable. Each batch receives a unique lot number with sufficient retention samples maintained in accordance with Cosperpharm quality procedures.

Stability monitoring program. Cosperpharm conducts ongoing stability studies under recommended storage conditions: long‑term storage at –20 °C under inert atmosphere. Shelf life: 3 years at –20 °C.

Documentation ready for regulatory submission. Every shipment includes a Certificate of Analysis (COA) with batch‑specific purity and characterization data, a Material Safety Data Sheet (SDS), and customs documentation for international delivery. For customers preparing peptide API regulatory submissions, Cosperpharm provides DMF‑ready documentation packages, method validation reports, stability data, and custom quality agreements upon request.

Customer‑initiated quality audits. Qualified customers are welcome to audit Cosperpharm‘s manufacturing, quality control, and documentation facilities. ISO compliance documentation is available upon request.

Contact us

Need a consistent and high‑purity supply of Fmoc-Arg(Pbf)-OH for your peptide synthesis program? Contact Cosperpharm today to discuss your requirements and request a quote.